Embodiments of the present invention relate generally to techniques including a method and a structure for forming substrates using a layer transfer technique. Certain embodiments employ an accelerator process for the manufacture of semiconductor films in a variety of applications including optoelectronic devices such as light emitting diodes (LEDs) and semiconductor lasers. But it will be recognized that the invention has a wider range of applicability; it can also be applied to other types of applications such as for three-dimensional packaging of integrated semiconductor devices, photonic or photovoltaic devices, piezoelectronic devices, flat panel displays, microelectromechanical systems (“MEMS”), nano-technology structures, sensors, actuators, integrated circuits, biological and biomedical devices, and the like.
Certain embodiments may including methods and apparatuses for cleaving free standing films from material in bulk form, such as a single crystal silicon ingot or a GaN ingot. Such free standing films are useful as a template for the formation of an optoelectronic device such as an LED. But, it will be recognized that embodiments of the invention have a wider range of applicability; it can also be applied to other types of applications such as for three-dimensional packaging of integrated semiconductor devices, photonic devices, piezoelectronic devices, flat panel displays, microelectromechanical systems (“MEMS”), nano-technology structures, sensors, actuators, integrated circuits, biological and biomedical devices, and the like.
Semiconducting materials find many uses, for example in the formation of logic devices, solar cells, and increasingly, illumination. One type of semiconductor device that can be used for illumination is the light emitting diode (LED). In contrast with traditional incandescent or even fluorescent lighting technology, LED's offer significant advantages in terms of reduced power consumption and reliability. Another type of semiconductor device that can be used for illumination is a laser. Lasers that operate based upon semiconductor principles are finding increasing adoption for use in displays and other applications.
Such optoelectronic devices rely upon materials exhibiting semiconductor properties such as silicon and also type III/V materials such as gallium nitride (GaN). Silicon is often made using either polysilicon (i.e. polycrystalline silicon) and/or single crystal silicon materials. GaN is also available in various degrees of crystalline order. However, these materials are often difficult to manufacture.
Additionally, both silicon and other semiconducting materials suffer from material losses during conventional manufacturing called “kerf loss”, where the sawing process eliminates as much as 40% and even up to 60% of the starting material from a cast or grown boule and singulate the material into a wafer form factor. This is a highly inefficient method of preparing expensive semiconducting materials for optoelectronic applications.
In particular, conventional techniques for manufacturing single crystal silicon or other semiconductor materials into electronic devices, typically involve the physical separation of thin single crystal silicon layers or layers of other semiconductor materials, from an originally grown ingot or boule. One such a conventional manufacturing technique is inner diameter (ID) sawing.
The ID sawing technique employs a circular saw having a blade located on its inner diameter. The ingot is pushed through the center of the saw until a desired wafer thickness is on the other side of the saw. With the saw rotating, the saw is then raised or lowered to allow the blade to slice through the ingot. The ID sawing method offers a number of possible disadvantages.
One is that the saw must be of minimum thickness to be sufficiently strong to withstand the stress of the sawing action. However, an amount of silicon material corresponding to this saw thickness (the kerf) is lost by this cutting. Use of even the thinnest saw blade that can reliably be used to saw the ingot, may result in losses of expensive, pure single crystal silicon to the kerf. For example, a typical saw blade kerf has a width of 300 μm, where an individual sliced wafer may have a width of only 800 μm. Use of the conventional wafer sawing technique can thus result in kerf losses of expensive, pure starting material amounting to as high as 60% of the entire ingot. Another disadvantage of the conventional ID sawing technique is that slices can only be separated one at a time, thus limiting throughput and elevating cost.
Partly in response to the limited throughput of sawing, the alternative conventional technique of wire sawing has been developed. In wire sawing, a network of rapidly moving parallel wires is provided. The side of an ingot is then contacted with the moving wires in an environment including oil and abrasives, resulting in simultaneous slicing of the wafer into a plurality of wafers. The advantages of this technique over ID sawing includes parallel sawing of the boule and producing thinner wafers of 180-250 um with a more modest 190-250 um kerf loss. While effective, conventional wire sawing also offers disadvantages, in particular a still significant kerf loss of about 50% attributable to the thickness of the wire, and possible contamination by exposure of the substrate to the oil and abrasives.
From the above, it is seen that techniques for forming suitable substrate materials of high quality and low cost are highly desired. Cost-effective and efficient techniques for the manufacture of semiconductor-based optoelectronic devices are also desirable.